The present invention relates to a coating composition for vibration damping and a method for producing the same, more particularly a coating composition capable of forming a damping film over a vibration- or sound-generating portion of an automobile, building, various industrial machines and facilities, home electronic appliances, medical equipment, among others, to absorb vibration or sound generated at such a portion, particularly efficiently in a low frequency range and also efficiently even in a high frequency range.
Formed articles, such as plate- and sheet-shaped articles, of materials having vibration- or sound-absorbing materials, have been proposed as damping materials. However, when a portion at which vibration or sound is generated has a complex shape, the above damping material cannot sufficiently exhibit its inherent damping effect, because of significant difficulties in application of the material to such a shape. In order to overcome these difficulties, various types of coating materials have been proposed to realize the vibration- or sound-absorbing effect by the films of such materials spread over the portion in question by an adequate method, e.g., spraying. These coating materials for damping purposes include aqueous coating materials comprising, e.g., asphalt, rubber or synthetic resin as the extender incorporated with a synthetic rubber powder to improve coating film hardness, and resin emulsions dispersed with activated carbon as the filler, which serve as the coating materials suitable for automobile interiors.
However, many of the conventional coating compositions for damping purposes are reinforced for the vibration-absorbing effect of the film-forming component with an inorganic powder or the like, which has failed to greatly improve the vibration- or sound-absorbing effect of the film-forming component itself. When the damping material is used in the form of film, its thickness is limited normally to 2 mm or less, particularly 1 mm or less. However, it is found that the damping film loses loss factor xcex7 rapidly as its thickness decreases, making it difficult to efficiently absorb vibrational or acoustic energy from the outsides. Under these developmental situations, development of a coating material which can exhibit high degree of damping effect even by the thin film has been keenly in demand.
It is an object of the present invention to provide a coating composition for damping purposes, capable of forming the damping film excellent in vibration- and sound-absorbing effects and having loss factor xcex7 as the vibration absorption evaluation index not extremely decreasing as its thickness decreases, in consideration of the above situations.
It is another object of the present invention to provide a coating composition for damping purposes which is formed into the damping film capable of contributing to improved efficiency of vibration- and sound-absorption in both low and high frequency ranges, even when the film is thin.
Also it is another object of the present invention to provide a method for producing the coating composition for damping purposes, capable of forming the damping film excellent in vibration and sound absorbing effect.
The inventors of the present invention have found, after having extensively studied to improve loss factor h of the thin film as the object of this invention, that loss factor h largely depends on the product of loss modulus Exe2x80x3 and film thickness xe2x80x9ct,xe2x80x9d by which is meant that it is essential to increase loss modulus Exe2x80x3 in order to improve loss factor h at a certain film thickness or to secure a high loss factor h by the thin film. They have grasped, based on the above knowledge, that the coating film comprising a resin emulsion containing a polar group has an increased content of the hydrogen bonds when the emulsion is incorporated with a component having ability of forming the hydrogen bond (hereinafter referred to as xe2x80x9chydrogen bond forming componentxe2x80x9d) and the hydrogen bond content can be controlled, and that the coating film having the controlled content of the hydrogen bonds has a high loss modulus Exe2x80x3 giving a high loss factor h even when the film is thin and has excellent effects of absorbing vibrational and acoustic energy from the outsides.
The inventors of the present invention have further investigated the above phenomena to find the cycles that, when vibrational/acoustic energy from the outsides enters the coating film, the hydrogen bond formed while the coating film absorbs the energy is dissociated, and formed again after the energy generated while the hydrogen bond is restored is released as heat, and also find that the coating film has an increased loss modulus Exe2x80x3 and loss factor ii, as the hydrogen bond forming effect of the hydrogen bond forming component increases, heat of the dissociation increases, or the hydrogen bond of adequate strength is formed. They have also found that the coating film shows the high damping effect, when it has the hydrogen bond whose intensity is controlled in response to intensity of the vibrational energy from the outsides, reaching the present invention.
The first invention relates to a coating composition for damping purposes, which comprises the following coating components (i), (ii) and (iii):
(i) a resin emulsion containing a polar group capable of forming the coating film containing the hydrogen bond which is formed when the polar group comes into contact with an aromatic compound as the following coating component
(ii) having the hydrogen bond forming effect,
(ii) an aromatic compound which has the effect of forming and controlling the hydrogen bond, and also has at least one hydroxyl group in the molecule, and
(iii) an inorganic filler.
The second invention provides a coating film for damping purposes which is formed using the above coating composition, having a loss factor xcex7 at a coating film thickness of 2 mm or more, and 0.03 or more and 0.065 or more at frequency of 50 and 1200 Hz, respectively.
The third invention relates to a method of producing a composition for damping purposes, which comprises the following steps (1) and (2):
(1) a step of dispersion and mixing the above-described coating components (i) and (ii) with each other, and
(2) a step of mixing the above mixture with the above-described coating component (iii).
The present invention also provides a method of producing the above-described coating composition for damping purposes, which comprises the following 2 steps;
(1) a step of bringing the above-described coating component (ii) into contact with the above-described coating component (iii) in the presence of a solvent which can dissolve the coating component (ii), and thereby impregnating the coating component (iii) with the coating component (ii), and
(2) a step of mixing the resultant impregnated component with the above-described coating components (i).
The present invention also provides a method of producing the above-described coating composition for damping purposes, which comprises the following 2 steps;
(1) a step of bringing the above-described coating component (ii) into contact with the above-described coating component (iii) in the presence of a solvent which can dissolve the coating component (ii), and thereby impregnating the coating component (iii) with the coating component (ii), and
(2) a step of mixing the resultant impregnated component with the above-described coating components (ii).
As described above, the present invention relates to a coating composition for damping purposes, capable of forming the coating film containing the hydrogen bond, and the preferred embodiments include the following compositions (1) to (5):
(1) A coating composition for damping purposes, comprising 20 to 70% by weight of an acrylic resin emulsion, 2 to 30% by weight of a phenolic compound represented by the general formula (III), 15 to 50% by weight of mica, and a dispersant, flow improver, thickening agent and viscosity adjusting agent.
(2) A coating composition for damping purposes, comprising 20 to 70% by weight of an acrylic resin emulsion, 2 to 30% by weight of a phenolic compound represented by the general formula (III), 15 to 50% by weight of montmorillonite, and a dispersant, flow improver, thickening agent and viscosity adjusting agent.
(3) A coating composition for damping purposes, comprising 20 to 70% by weight of an ethylene/vinyl acetate copolymer emulsion, 2 to 30% by weight of a naphthalene-based compound represented by the general formula (II), 15 to 50% by weight of saponite, and a dispersant, flow improver, thickening agent and viscosity adjusting agent.
(4) A coating composition for damping purposes, comprising 20 to 70% by weight of an ethylene/vinyl acetate copolymer emulsion, 2 to 30% by weight of a phenolic compound represented by the general formula (III), 15 to 50% by weight of mica, and a dispersant, flow improver, thickening agent and viscosity adjusting agent.
(5) A coating film for damping purposes, comprising one of the above-described coating compositions (1) to (4), having an infrared absorption intensity (1720 to 1690 cmxe2x88x921)/infrared absorption intensity (1750 to 1720 cmxe2x88x921) ratio of 0.2 or more and loss modulus Exe2x80x3 is 1.08xc3x97108 Nxc2x7mxe2x88x922 or more.